Dosimetric Comparison Of Incidental Radiation To The Internal Mammary Nodes After Breast-conserving Surgery Using Three Techniques:I-IMRT,F-IMRT And 3D-CRT

Objective:To explore the dosimetric variance of incidental irradiation to internal mammary nodes among inverse intensity-modulated radiotherapy?I-IMRT?,field-in-field intensity-modulated radiotherapy?F-IMRT?and three-dimensional conformal radiotherapy?3DCRT?for patients after breast-conserving surgery.Methods:A total of 84 patients with breast-conserving surgery underwent CT simulation,and internal mammary region including the first three intercostal spaces was contoured.Three different plans were created by one physicist.For the patients with a tumor bed,all three plans incorporated the simultaneous integrated boost?SIB?technique,and the whole breast and tumor bed were treated with 1.8 Gy and 2.15 Gy,respectively,in 28 fractions for a total dose of 50.4Gy and 60.2Gy,respectively.For the patients who underwent radiation for the whole breast only,a common radiotherapy strategy of 50 Gy/25 F to the whole breast was adopted.The internal mammary region was not included in the planning target volume.Results:The median mean doses(D_mean)of the first three intercostal space were 2740.2cGy,2 973.9cGy and 2 951.4cGy for I-IMRT,F-IMRT and 3DCRT,respectively.The differences were not detected between any of the plans.Separating the three intercostal spaces to analysis,the mean doses of the first two intercostal spaces were both not significantly different between any of the plans.However,for the third intercostal space,the median Dmean was highest for the I-IMRT,and the differences were not detected between the 3DCRT and F-IMRT.Separating the three techniques to analysis,the median D_mean were highest in the third intercostal space,followed by the second intercostal space and lowest in the first intercostal space.Conclusions:All the three techniques fail to attain an adequate dose to cure subclinical disease and there was not significant difference among the three techniques.It is risky to avoid IMNI using any of the three techniques during whole breast radiotherapy in women with indications for elective IMNI.However,in systematic therapy,whether the incidental dose could meet clinical acquirement need further follow-up.